1. Field of the Invention
The present invention relates to a portable telephone radio set to which a terminal equipment as represented by a personal computer is connected to effect data communication therewith.
2. Description of the Related Art
In recent years, a portable telephone radio set is used frequently such that a terminal equipment such as a personal computer is externally connected thereto to effect data communication therewith. However, the portable telephone radio set is liable to be subject to radio wave interference from the terminal equipment externally connected thereto and suffer from deterioration of the communication quality. Further, data communication is different from communication by voice, which allows confirmation with the ear, in that, even if the communication quality is deteriorated, this cannot be recognized readily by a user of the portable telephone radio set.
Conventionally, as regards a portable telephone radio set of the type described such as, for example, a portable telephone radio set which complies with the RCR STD-27 standard published by the Association of Radio Industries and Business (ARIB), a standard is available which relate to a waiting-switching operation, after the power supply to the portable telephone radio set turned on, of the mobile station when a used channel set from a base state is in a wait state.
A procedure on the mobile state base on the standard is illustrated in FIG. 4. First, when the power supply is turned on, perch channels which form a group are scanned to measure the level of each of the channels (step S1), and a channel table in which the levels are arranged in order of the level is prepared (step S2).
Then, the mobile station searches for those perch channels each having a level higher than a predetermined level from within the channel table prepared in this manner (step S3). If perch channels having a level higher than the predetermined level are detected (YES in step S4), then one of those perch channels is selected in accordance with a predetermined method (step S5), and a signal of the selected perch channel is received (step S6). Then, information of the layer 1 and broadcast information are detected from within the received signal and analyzed (step S7), and if a waiting condition is satisfied (YES in step S8), then the processing advances to operation during the waiting state (step S9).
If the discrimination in step S8 is “NO” since the waiting condition is not satisfied, then the remaining perch channels each having a level higher than the predetermined level are investigated from within the channel table (step S10). Then, the processing returns to step S4 described above. Thus, the succeeding steps are repeated until the discrimination in step S4 becomes “NO” because a perch channel having a level higher than the predetermined level does not remain any more.
If the discrimination in step S4 is “NO” because there remains no perch channel having a level higher than the predetermined level, then it is determined that the mobile station is in an out-of-zone state (step S21). Then, the processing returns to step S1, in which scanning of perch channels of a next group is started.
In the conventional portable telephone radio set described above, if interruption of communication or failure in connection is caused by radio wave interference and deteriorates the communication state, then since the user of the radio set cannot recognize that data communication on the terminal equipment has entered an incomplete state, there is a problem that increase of the communication time by unnecessary requests for retransmission, increase of the communication fee by unnecessary retransmission processing and so forth occur.
The reason is that the conventional portable telephone radio set does not have a function for directly reporting deterioration of the communication state caused by radio wave interference to the user of the portable telephone radio set.